Ring opening mechanisms of naphthenic jet fuels in the pyrolytic regime

摘要

Structural rearrangement from traditional paraffinic-based jet fuels to naphthenic hydrocarbons can greatly enhance the thermal stability of the jet fuel when used as a coolant under pyrolytic conditions (1,2). The advantage of cyclic structure is their ability to resist ring opening reactions during high thermal stress when compared to the low temperature rupture of long-chain alkanes (3). Although the propagation reactions under pure pyrolytic conditions are well understood and can be controlled for paraffinic compounds by the use of hydrogen donors, such as tetralin (4) and alpha-tetralone (5), very little is known about the ring opening mechanisms of cyclic compounds. Some studies have shown that in the pyrolytic region naphthenic model compounds such as decalin may experience ring opening, undergo isomerization or become dehydrogenated (6,7). Especially the ring opening mechanism is of great concern towards the design of thermally stable jet fuels due to the subsequent formation of aromatic that can lead to solid deposit (8). However, to control these mechanisms a deep understanding of the reaction pathways is needed. Accordingly, this work has studied the reaction chemistry during ring opening of model compound for naphthenic jet fuels in the autoxidative anhd pyrolytic regimes using a flow-reactor. At very high temperatures above 700 deg C cyclic structures such as decalin tend to open one ring that promotes the formation of one-ring aromatic compounds. The mechanisms were found to involve the stable 3 deg free radical that differ from the 1 deg and 2 deg typically observed in paraffinic fuels.